Today, several manufacturers propose radiocommunication circuits (communicating modules) that have the capacities for detecting scrambling to their customers.
The current technique for detecting scrambling by these radiocommunication circuits consists in carrying out a complete diagnostic of the radio environment and, according to the result of this diagnostic, in providing a status of the type: “the network is scrambled” or “the network is not scrambled”.
The problem with the current technique is that the complete diagnostic of the radio environment takes a non-negligible amount of time. The consequence is that, when a scrambling is detected, the corrective actions (in general linked to security) can in certain cases be launched too late.
This problem is now shown by using the example of devices for recovering stolen cars. Typically, such a device comprises:                a radiocommunication circuit (for example a GSM module), making it possible to communicate with a theft management server in order to roll up/recover information;        a GPS module, making it possible to obtain the position of the vehicle; and        a security module, making it possible to immobilize the vehicle (activation of an ignition cut-off), trigger an alarm or carry out any other action making it possible to limit the access or the use of the vehicle by the possible thief.        
If the radiocommunication circuit does not support the capacity for detecting scrambling, the device for recovering can be rendered entirely ineffective by the simple presence ad vitam of a scrambler which can be connected to the cigarette lighter. Indeed, if the device has not detected the intrusion and the theft of the car, no longer receiving any message via the radiocommunication network, it can no longer be informed by the theft management server that the car is stolen and as such cannot activate the ignition cut-off or the alarm, and is therefore completely ineffective.
If the radiocommunication circuit supports the capacity for detecting scrambling, the supplying by the radiocommunication circuit of the “the radiocommunication network is scrambled” information can take several dozens of seconds. Indeed, as indicated hereinabove, during the loss of synchronization with the radiocommunication network, the radiocommunication circuit launches a complete diagnostic of the radio environment and at the end of this diagnostic provides its conclusion: “the radiocommunication network is scrambled” or “the radiocommunication network is not scrambled”. This diagnostic can take 40 seconds in the case of a GSM network for example. During this time, the thief can enter into the car and start it. Or, once the car is started, the device, for obvious reasons of road safety, is no longer legally authorized to trigger the ignition cut-off. On the other hand, as it is scrambled, the radiocommunication circuit can no longer communicate with the theft management server. The thief can therefore drive the car to a secluded area, where he can easily find the device for recovering stolen cars and deactivate it.
This discussion, provided simply by way of an illustrative example, can of course be transposed to other applications based on a radiocommunication circuit: alarms, systems for following (“tracking”) containers, etc.
Patent application WO 2005/112321 A1 (filed by the DAI TELECOM company) has an example of implementing the aforementioned current technique for detecting scrambling. The complete diagnostic of the radio environment carried out by the radiocommunication circuit consists in:                detecting the verification of the following condition: there is a number DCMN (“Disturbed Channels Minimum Number”) of radiocommunication channels whereon the radiocommunication circuit cannot be synchronized despite the detection of a power level greater than a predetermined MNPL threshold (“Maximum Noise Power Level”) above which it is normally possible to be synchronized;        if said condition is verified, generation of a scrambling signal, in the form of a JDR message (“jammed condition report”) which is transmitted to the base station, for example via a RACH access channel (“Random Access Channel”) or PRACH (“Packet Random Access Channel”).        
The parameter DCMN is frozen (for example at 5). The parameter MNPL is also frozen, and fixed by the operator of the network, for each cell. These two parameters are used to finely adjust the algorithms for detecting scrambling, and their values are factory-adjusted and must not normally be modified (except if the mobile is installed in a particular environment, the default values can then be modified in order to be adapted to this particular environment).
It is important to note that in the current technique (including that of application WO 2005/112321 A1), the detecting of scrambling comprises a single detection phase of the complete diagnostic of the radio environment. The decision taken at the end of this single detection phase is therefore a final decision. In other terms, at the end of the complete diagnostic, the result provided is:                either a signal indicating that “the network is not scrambled”, with a probability of scrambling of 0%;        either a signal (called scrambling signal) indicating that “the network is scrambled”, with a probability of scrambling of 100%.        
As such, in the current technique, the choice of the number of radiocommunication channels “that cannot be synchronized” whereon is taken the decision for detecting scrambling (i.e. the parameter DCMN in the particular case of application WO 2005/112321 A1) is not optimal since it is the result of a compromise between on the one hand the reliability of the detecting of scrambling and on the other hand the rapidity of the decision:                this number (DCMN) must not be too small, which could result in the triggering of false detections of scrambling (it may be normal that there are a few radiocommunication channels whereon the radiocommunication circuit cannot be synchronized, but that does not necessarily means that a synchronization is not possible on another radiocommunication channel);        this number (DCMN) must not be too big, which could result in the complete diagnostic of the radio environment taking a period of time that is too long.        
The current technique (including that of application WO 2005/112321 A1) is therefore not optimal since it either favors a decision (of detection of scrambling) that is rapid but to the detriment of quality, or it favors a sure decision but which may be too slow.
Furthermore, the current technique, due to the fact that no decision relative to a possible scrambling is taken before the end of the complete diagnostic of the radio environment, does not allow for the launching of preventive actions.